The planned research for the coming year includes the following: 1) A continuation of the description of cortical cells which give rise to the descending corticofugal fibers. Thus, HRP will be injected into not only the LGD and LP but the pretectal nuclei and the SC as well, and the cortices will be processed to reveal cells projecting upon these structures. 2) A continuation of the investigation of the tectothalamic fiber projections utilizing both autoradiographic and retrograde transport techniques. 3) The initiation of experiments designed to more closely relate tectothalamic fiber terminals to the thalamic cells, particularly within the LP, which project to the visual cortex. In this regard, injection of 3H-leucine in the superior colliculus will be paired in the same animal with cortical injections of HRP. Tissue sections will be processed for HRP histochemistry, slide mounted, then processed by autoradiographic methods. Thus, individual sections will hopefully contain retrogradely HRP-filled thalamocortical cells and labelled techtothalamic terminals; and the anatomical relationship of these two can then be studied.